In the tech world today, a common strategy for dealing with problems is to simply throw “more” at them. When cell phone manufacturers realized we wanted to take selfies, the earliest solutions were cameras that could swivel around. Now, they just slap a camera on the front in addition to the one on the back. When roboticists want to add complex motion to a robot, they usually just add more motors. Disney Research is taking a more clever approach that utilizes sophisticated linkages for fluid bipedal movement.
You can make a bipedal robot walk with just two motors and two degrees of freedom in each leg, but that results in an awkward, clumsy gait. To get smoother movement, most roboticists add more motors to gain more joints. The idea is to create a more natural gait, but nature doesn’t take that approach with animals. If you think of your muscle pairs as “motors,” your legs only have a few. The reason you’re able to walk efficiently is because of the opposing tension of muscles and tendons, not because your legs have many degrees of freedom.
Disney Research’s “Serial-Parallel Hybrid Leg Mechanism” takes a similar approach, and the results are impressive. This leg mechanism has six degrees of freedom, like many other bipedal robots, but places all but one of the motors in the hips. Those motors move the leg through clever linkages that give the robot a smooth, natural gait. The design keeps the center of gravity close to the pelvis, just like the human body. The robot can walk extraordinarily well, and contains most of the motors in one efficient area.